The invention relates to high-pressure viscous dampers. Viscous dampers serve to absorb short-term feed variations in fluid systems in order to avoid undesired excessive pressure rises and to average a pulsating feed of fluid. To this end, known viscous dampers are constructed with first and second chambers separated by an elastic partition or membrane, one chamber receiving the fluid to be damped with respect to pressure and flow variations and the second chamber holding a damping fluid. A temporarily increased feed of fluid results in a pressure rise which is absorbed by the damping fluid via the elastic partition. If less fluid is conveyed temporarily, the pressure sinks and the damping fluid expands and compensates for the lacking volume.
In liquid chromatographs viscous dampers serve to equalize the flow of a solvent through a separating column, because flow variations affect the measuring accuracy disadvantageously. Moreover, it is extremely important that the chambers through which the solvent flows have a dead volume as small and constant as possible. For example, at a feed rate of one hundred microliters per minute which at today's standards is not unusual for the achievement of high sensitivity, a few microliters of dead volume have an extremely negative effect.
The known high-pressure viscous dampers do, however, have the disadvantage that their dead volume changes with temperature. Because of the different temperature expansion coefficients and because of the materials involved, a temperature change leads to a change in pressure with an accompanying change in volume of the second chamber by deformation of the elastic partition. Consequently, the dead volume represented by the first chamber also changes. Particularly the known fluids which are sufficiently compressible for damping purposes (e.g. Hexane) have a substantially higher temperature expansion coefficient than the metals used for the housing of such dampers (e.g. steel).
In the known high-pressure viscous dampers, the damping fluid is therefore filled into the housing at a relatively high temperature of approximately 40 degrees centigrade and this temperature is maintained during operation by way of thermostats. This leads to quite substantial problems regarding temperature sensitivity of some solvents, and the regulation of temperature requires some additional expenditure.